8274
J. Am. Chem. SOC.1985, 107, 8274-8276
irradiated by room fluorescent light. Another identical solution was stored in the dark. At given intervals of time, 2OO-gL aliquots of the irradiated reaction solution were transferred under N, to 2-mL capsealed bottles with a gas-tight syringe and these samples were stored on dry ice. Each sample was carefully (to avoid light) analyzed by H P L C 6 The results are shown in Figure 1. Inspection of Figure 1 shows that the plots of the yields of benzaldehyde and DA vs. irradiation time exhibit the shape anticipated for an autocatalytic reaction. Analysis of the reaction solution stored in the dark after 4.5 h showed that no benzaldehyde or DA had been formed. Irradiation of this solution provided a quantitative yield of benzaldehyde and DA after 40 min. In a separate experiment, a solution of (TPP)Cr"'Cl (8.0 X lod M) and N O (1.1 X lo4 M) in CH2C1,was subjected to intermittent exposure to room fluorescent light followed by monitoring in the dark at 429 nm. It was found that the reaction continued for up to 2 min in the dark after each period of light exposure. In order to determine if DA, a product of oxygen transfer from NO, might play a role as an autocatalytic agent, the experiment of Figure 1 was repeated with the inclusion of 1.2 X M DA. The time course for this reaction was followed by HPLC analysis of benzaldehyde and is included in Figure 1. By inspection of the figure there is seen to be a shortening of the lag phase and a small rate enhancement. DA seems to play some minor role in the photoinduced autocatalysis. That (TPP)Cr"O is not the oxidant for the rapid reaction with PED reported above is shown by the following experiments. The formation of benzaldehyde was followed by HPLC after mixing of a solution composed of (TPP)CrIVO(4.52 X M) and a 100-fold excess of PED in CH2Cl2. After 24 h there still remained more than 50% of unreacted (TPP)CrIVO. This result establishes that the oxidation of PED by ground-state TPPCrlVOis far too slow to be a competent component of the mechanism of the photocatalytic reaction, since the photocatalytic reactions of Figure 1 go to completion in a short period of time. The species (TPP)CrIVOis a rather stable oxo metalloporphyrin as shown by the fact that it has been isolated and characterized by X-ray crystallography.' Though this species is known to oxidize alcohols to aldehydes the rate of reaction with PED is, as shown, quite slow. The species (TPP)(C1)CrVOis a much stronger oxidizing agent* than (TPP)Cr"O and is stable in CH2C12for a few hours at room temperat~re.~Controlled-potential oxidation of (TPP)CrrVOwas used to provide a stable CH,Cl2 solution of (TPP)(C104)CrV0 M). To this solution there was added PED (to a (4.4 X concentration of 6.2 X M) and the decrease in (TPPj(C1OA)CrVO(412 nm) and increase in (TPP)Cr"'ClO, (450 nm) was fdiowed at 30 ' d i n the dark. The reaction was-found to'obey the first-order rate law (/cobs,, = 6.7 X lo-, s-l) and the isosbestic points at 374 and 439 nm established the absence of any accumulated intermediate. The oxidation of PED produced quantitative yields of benzaldehyde (95% by HPLC)6 and formaldehyde (100% by Nash procedure).1° The rapid rate of reaction of PED with the oxo-CrV porphyrin species allows this reaction to be a competent component of the photocatalysis of PED oxidation by NO. We have shown (loc. cit.) that both (TPP)CrTVOand (TPP)(C1)CrVOare present following the irradiation of solutions of (TPP)Cr"'Cl and NO. The formation of (TPP)CrIVOis known3 to occur by disproportionation of (TPP)Cr"'Cl with (TPP)(C1)Cr"O. High monooxygen donation potential compounds react with (TPP)Cr"'Cl to afford principally (TPP)(C1)CrVOand low monoxygen donation potential compounds can only afford (TP(6) HPLC was performed as described in ref IC. The retention time of each product follows: benzaldehyde ( 5 . 5 min), DA (8-9 min), andp-cyanoN-methylaniline (20 min). (7) Budge, J . R.; Gatehouse, B. M . K.; Nesbit, M. C.; West, B. 0. J . Chem. SOC.,Chem. Commun. 1981, 370. (8) (a) Groves, J. T.; Kruper, W. J., Jr. J . Am. Chem. SOC.1979, 101, 7613. (b) Groves, J. T.; Haushalter, R. C. J . Chem. SOC.,Chem. Commun. 1981, 1165. (9) Buchler, J . W.; Lay, K. L.; Castle, L.; Ullrich, V. Inorg. Chem. 1982, 21, 842. (10) Nash, T. Biochemistry 1953, 55, 416.
0002-7863/85/1507-8274$01.50/0
P)Cr"O. Since in the photocatalytic reaction the spectra of the spent reaction solution is that of both (TPP)(C1)CrVOand (TPP)Cr"O and the reaction of percarbxylic acids with (TPP)Cr"'Cl provides a similar composition of Cr(1V) and Cr(V) species,l we may conclude that the photocatalytic oxygen transfer from N O to (TPP)Cr"'CI is as efficient as the oxygen transfer from percarboxylic acids to (TPP)Cr"'Cl in the dark. Though the nature of the photoautocatalysis is not understood the essence of the overall oxidation of PED may be expressed as shown in eq 1-3. (TPP)Cr"'CI
--+
+ NO
hu
(TPP)(Cl)CrVO+ (TPP)Cr"'Cl-
+
(TPP)(Cl)CrVO PED (TPP)Cr"'Cl
(TPP)(C1)CrVO + DA (1) HZO
PhCHO
2(TPP)CrlV0 + 2HC1 (2)
+ HCHO + H 2 0 ( 3 )
In summary, unlike the facile and dark transfer from NO to iron(II1) and manganese(II1) meso-tetraphenylporphyrins, the oxygen transfer to chromium(II1) occurs only by photocatalysis. While aniline N-oxides have been shown to undergo photoinitialized deoxygenation," it has been demonstrated previously that p-cyano-N,N-dimethylaniline N-oxide does not react with our trap (PED).3 While the product of the photocatalysis oxidizes PED very rapidly, (TPP)CrLVOdoes not; and since (TPP)(C1)CrVO does, the latter must be the initial product of oxygen transfer and, thus, is converted to (TPP)CrlVOby comproportionation with (TPP)Cr"'CI. Acknowledgment. This work was supported by a grant from the National Institutes of Health and The American Cancer Society. (1 1) (a) Stenberg, V. I.; Schiller, J. E. J . A m . Chem. Soc. 1975, 97,424. (b) Stenberg, V. I.; Schiller, J. E. J . Org. Chem. 1973, 38, 2566.
A Vinyltrimethylenemethane Intermediate in the 1,3-Sigmatropic Rearrangement of the 6-Methylenebicyclo[3.l.0]hex-2-enylSystem Steven Pikulin and Jerome A. Berson* Department of Chemistry, Yale University New Haven, Connecticut 06511 Received September 9, 1985 Because the barriers to internal rotation and cyclization of biradicals usually are very the identification of these species as true intermediates in thermal rearrangements has been difficult. We conjectured that a stabilizing structural alteration of the biradical should deepen the local potential minimum and facilitate detection of the intermediate. This paper describes the experimental consequences of such an alteration, in which the putative partially conjugated biradical 1 of the bicyclo[3.1 .O]hex-2-ene rearrangement6-*is converted to the fully conjugated vinyltrimethylenemethane (VTMM) species 2 derived from 6(1) Dervan, P. B.; Dougherty,, D. A. In "Diradicals"; Borden, W. T., Ed.; Wiley: New York, 1982; p 107. (2) Doering, W. v. E. Proc. Natl. Acad. U.S.A. 1981, 78, 5279. (3) Gajewski, J. J. "Hydrocarbon Thermal Isomerizations"; Academic Press: New York, 1981. (4) Berson, J. A. In "Rearrangements in Ground and Excited States"; de Mayo, P., Ed.; Academic Press: New York, 1980; p 311. ( 5 ) Doubleday, C., Jr.; McIver, J . W., Jr.; Page, M. J . Am. Chem. SOC. 1982, 104, 3768, 6533. (6) Doering, W. v. E.; Schmidt, E. K. G. Tetrahedron 1971, 27, 2005. (7) Cooke, R. S.; Andrews, U. H. J . Am. Chem. SOC.1974, 96, 2974. (8) Swenton, J. S.; Wexler, A. J . Am. Chem. SOC.1971, 93, 3066.
0 1985 American Chemical Society
J. Am. Chem. Soc., Vol. 107, No. 26, 1985 8275
Communications to the Editor methylenebicyclo[3.1 .O]hex-2-enes9*10
Scbeme I
Hg < ,
R
Hg
R 1 R
R
R
R 2
Reduction of ketone 311to the syn alcohol 4 with DIBAH12a followed by methylation gave the syn methyl ether 5.I3,l4 Acid-catalyzed equilibration of the syn-anti (4-6) alcohol mixture
8 I
\
Hb
Ha L : X - OH 5 : X = OMe
3
X Hb 6 : X - OH 7 : X = OM@
obtained by Luche reduction12bof 3 gave the more stable anti alcohol 6, which upon methylation gave anti methyl ether 7.15 Heating either 5 or 7 in benzene (54-140 "C) led to a highly stereoselective rearrangement to the endo and exo cyclopropyl methyl ethers 8 and 916(Scheme I) in a ratio of ~ 3 O : l . lControl ~ experiments demonstrated that 8 and 9 do not interconvert under these conditions. A hypothesis of two pairs of competitive pathways from 5 and 7, without a common intermediate, would imply identical competition ratios in systems with entirely different geometric requirements for reactive atomic motions. More probably, both 5 and 7 give the common VTMM 10 by cleavage of the bridge bond. The rearrangement of the anti compound 7 is about 16 times faster than that of the syn isomer 5 at 100 "C: kt7 = 1013'4exp(-24700(cal/mo1/2.3R~, k ; = exp(26 600(cal/mo1)/2.3RT). Double epimerization 5 7 would have been difficult to observe during pyrolysis because kt7 >> kt5;if prominent, the reverse process, 7 5, should have been observable but was not seen. With a common intermediate 10,the phenomenological ratio k $ / k t 5 is the same as the mechanistic ratio k 7 / k 5(Scheme I). When combined with the constraints of microscopic reversibility and the information (above) that kq = [7]/[5] probably is greater than unity, the data indicate a high degree of stereoselectivity in the ring-closure reactions of the biradical intermediate 10: k_7/k-5 I 16 and k_,/k+ = 21.
-
-
(9) Rey, M.; Huber, U.A,; Dreiding, A. S. Tetrahedron Lett. 1968, 3583. (IO) Newman, M. S.; Vander Zwan, M. C. J. Org. Chem. 1974,39,761. ( I I ) (a) Rule, M.; M a t h , A. R.; Dougherty, D. A,; Hilinski, E. F.; Berson, J. A. J . Am. Chem. SOC.1981, 103, 720. (b) Rule, M.; M a t h , A. R.; Seeger, D. E.; Hilinski, E. F.; Dougherty, D. A,; Berson, J. A. Tetruhedron 1982, 38, 787. (12) (a) Cf. inter alia: Wilson, K. E.; Seidner, R. T.; Masamune, S. J . Chem. Soc. D 1970,213. (b) Luche, J.-L. J . Am. Chem. SOC.1978,100,2226. ( 1 3) New substances were characterized by elemental composition and by mass and N M R spectroscopy. (14) Stereochemistry was assigned to 5 by N M R coupling constant (JAB = 6.8 Hz) and by nuclear Overhauser enhancement (NOE) measurements (250 or 500 MHz, difference display, irradiated nucleus signal enhancement): H, -+ Hbr I 1%; Hb Ha, 9%; Hf -+ Hb, 4%; H f H,, 4%. ( I 5) Stereochemistry of 7 assigned by JAB < 0.5 Hz; NOE Ha Hb, 4%; HI Hb, 10%; Hb Ha, 3%; Hb HI, 7%. (16) Compound 8: J A B ?_ J A c = 6.5 Hz;N O E Hb H, Ha, 13%; H, Hb + H,, 15%; H, H,, 3%. Compound 9: J A B LZ JAc
